The CANUSA study originally reported the importance of total small-solute clearance in predicting survival of peritoneal dialysis (PD) patients. However, subsequent reanalysis of data from the CANUSA study clearly demonstrated that the predictive power for mortality in PD patients was largely attributable to residual renal function (RRF) and not to the dose of PD. While this should not lead to the assumption that the dose of PD is unimportant, it does clearly indicate that the contribution of residual renal clearance and PD clearance to the overall survival of PD cannot be considered equivalent. In a previous study, we also demonstrated the importance of loss of RRF in predicting a heightened risk of mortality and cardiovascular death in PD patients. In this review, we focus our discussion on the different potential mechanisms that explain the important link between RRF and cardiovascular disease and survival of PD patients. We provide evidence to explain why RRF is so important to patients receiving long-term PD treatment and why it should be regarded as the "heart" of PD.